Cyclobutene derivatives from addition of α-halogeno electrophilic olefins to ynamines

Article abstract of DOI:10.1016/S0040-4020(01)97530-1

Reaction of α-chloro- and α-bromoacrylonitrile, α-chloro- and α-bromoacrylic esters with diethylaminomethylacethylene and diethylaminophenylacetylene leads to cyclobutene derivatives of type 3 in high yields. Reaction of E- and Z-α-bromocrotononitrile takes place in a stereospecific way. A mechanistic scheme for a reaction sequence of cycloaddition and subsequent allylic isomerization is formulated on the basis of stereochemical and kinetic data. The halogen substituents of the cyclobutene derivatives are stereospecifically displaced by the OH or the OEt groups in solvolytic reactions, with retention of configuration. Methylenecyclobutene derivatives are obtained from the 3-methylcyclobutenes by elimination of hydrogen halide with potassium t-butoxide. Hydrolysis of the enamine function of the cyclobutenes leads to the corresponding cyclobutanones. The configurations of four pairs of cis-trans isomeric cyclobutenes have been established by ¹H- and ¹³C-NMR spectroscopy.